I flipped one, but I did it on purpose, just to see how stable the boat was, and it was very difficult. And, it flipped right-side up all on it's own. I could not make it stay flipped. I won't say it can't be flipped accidentally, but I can't imagine what you have to do for that to happen. We've taken my friends NuCanoe on Class iV whitewater several times, and it never flipped, even with two 200+ lb. men in it. But, nothing is 100%. But I am convinced that the NuCanoe is a close to it as you can get. I am personally not crazy about them, because they are not very maneuverable, and they are painfully slow to paddle, but they are the most stabile boat I have ever sat in, even including Jon Boats. Just my opinion. Your mileage may vary....